It is conventionally known that an exposure device equipped in an electro-photographic-type image forming apparatus uses a light-emitting-element group, such as a light-emitting-element array, in which a plurality of light emitting elements is arranged linearly. It is also known to acquire a correction value of the amount of positional deviation of the light-emitting-element group etc., and to use the correction value to perform image processing of adjusting the lighting timing and the light emitting amount of light emitting elements.